Electrical discharge machines are presently widely used for cutting and shaping many different electrically conductive materials or workpieces. These machines remove material from a workpiece by spark erosion as an electrode or a moving wire electrode is placed near the workpiece. Typically, the workpiece and the electrode are placed at different electrical potentials for causing the necessary spark therebetween and, also, causing the electroerosion. Many sparks are rapidly provided between the electrode and the workpiece thereby creating the cutting action.
A dielectric machining liquid such as oil or de-ionized water is typically provided for cooling the cutting area of the workpiece and electrode and to carry away the very small pieces of the workpiece created by the cutting action. If these particles are not properly carried away from the cutting area, the sparks occurring between the workpiece and the electrode cannot accurately be controlled and, as a consequence, accuracy is significantly diminished. Accordingly, a continuous supply of clean machining liquid is required during the machining process.
In the past, the machining liquid has been filtered using filter elements, for example, incorporating filter paper. However, these filters quickly clog causing substantial down time for removing and replacing the paper filters. They are also ineffective at removing micron size particulates because their pores are often larger than the particulates created by the electrical discharge machining.
More recently, ceramic cross flow filters have been used for filtering machining liquid of electrical discharge machines. Examples of such uses are disclosed in U.S. Pat. No. 4,839,488 and U.S. Pat. No. 4,859,324. However, although these filter systems solve some of the problems associated with paper membrane filters, they have shortcomings and drawbacks. These prior cross flow filter systems tend to quickly build up a particulate layer on and within the cross flow filter membrane which cannot be easily cleaned by merely back pulsing in a direction opposite the normal flow for filtering. Additionally, a satisfactory means of removing the particulates from the capacity tank is not provided. Further yet, a satisfactory means of causing the particulates in the capacity tank to quickly coagulate and settle is not provided.